Enamel strand conductor for pipe type cable



Jan. 5, 1965 L. MEYERHOFF ENAMEL STRAND CONDUCTOR FOR PIPE TYPE CABLE Filed Sept. 18, 1961 H4LF-IMRD 77EMPER COPPER WIRES INSULATED ONE FROM THE ofl/ER BY POLYURETHANE ENHMEL COATINGS INVENTOR. LOUIS MEYERHOFF ATTORNEYS United States Patent M 3,164,669 ENAMEL STRAND CONDUCTOR FOR PIPE TYPE CABLE Louis Meyerhoff, Metuchen, N.J., assignor to General Cable Corporation, New York, N.Y., a corporation of New Jersey Filed Sept. 18, 1961, Ser. No. 138,986 6 Claims. (Cl. 174-414) This invention relates to an improved concentric, stranded cable conductor for pipe type cable and to the method of manufacturing such cable.

It is an object of this invention to provide a concentrically stranded cable conductor, each copperv strand of which has a half-hard temper and which is insulated from adjacent strands by an enamel coating.

It is a further object of this invention to provide an improved method for making a concentrically stranded conductor of enamel insulated wire in which each wire has a half-hard temper.

In accordance with these objects, there is provided, in a preferred embodiment of this invention, a concentrically stranded cable conductor formed from copper wires having a half-hard temper. Each wire is insulated from adjacent wires by a polyurethane enamel insulation.

By this construction, the tensile strength required for pulling long lengths of the assembled cable into pipe is provided. The concentrically stranded conductor in which each strand is insulated one from the other eliminates I the proximity effect between adjacent cables. When the concentrically stranded cable is installed in a steel pipe, the skin effect remains at substantially the same magnitude as that of the cable in air, and the proximity effect remains zero in contrast to segmental conductor cable, the skin and proximity effects of which are approximately doubled over the air values when installed in steel pipe. 'Thus, the cumulative skin effect and proximity effect of the concentrically stranded conductor in a steel pipe will be of the same order of magnitude as a segmental conductor in the same environment. Also, the cumulative skin effect and proximity effect of enameled concentrically stranded conductor will be much lower than conventional concentrically stranded cable using bare wire when installed in steel pipe.

In accordance with the method of manufacture of the cable conductor, the wiresare formed of copper having a half-hard temper. The temper is obtainedby appropriate selection of the drawing operations. Each wire is coated with a polyurethane enamel and is baked at a low temperature to cure the enamel Without annealing the wire. Thus, the wires are not annealed during baking but remain in the half-hard temper condition to provide the requisite tensile strength required for this application.

The wires may then be stranded to form the cable conductor, the conductor insulated in conventional fashion and the cable drawn into steel pipe. The enamel insulates adjacent strands to give the requisite electrical performance and prevents contact of the copper wire with the insulating oil to ensure stability of the oil.

Since the reduction of the proximity effect and the skin effect can be accorded merely by an insulation barrier between adjacent wires, it is sufficient to coat only those strands which touch one another in the assembled cable.

Thus, an effective construction in a 127-strand conductor might be the following:

Center wirebare 6-wire 1ayer-all wires enameled 12-Wire layer-alternating bare and enameled l8-wire layerall wires enameled 24-wire layer-alternating bare and enameled 30-Wire layerall wires enameled 36-wire layer-alternating bare and enameled In order to eliminate the deleterious effect of the copper on the oil, the bare wires may be aluminum, tinned copper or copper coated with a lead-tin alloy.

This invention will be more readily understood by reference to the following description taken in combination with the accompanying drawings, of which:

FIG. 1 is a perspective view of a cable conductor fabricated in accordance with the present invention;

FIG. 2 is a schematic illustration of the method of enameling the Wire strands; and

FIG. 3 is aschematic illustration of the equipment used in manufacturing such cable useful innexplanation of the method of manufacture. a

Referring to FIG. 1 there is shown a cable conductor 10 comprised of a plurality of individual wires 12 stranded in conventional fashion to form a concentrically stranded conductor. Each Wire 12 is copper having a half-hard temper so that the conductor will have the requisite'tensile strength to withstand the tensile stress applied during pulling of the cable into pipe. Since long lengths of cable, such as 3000-ft. lengths, must be pulled into pipe, the half-hard temper of the conductor wires is essential to provide requisite tensile strength.

The individual wires are insulated one from the other by an enamel insulating coating. This enamel is a poly-1 urethane enamel applied to each wire prior to stranding into'the conductor. The polyurethane enamel is bakedto cure the enamel. However, the baking temperature is maintained below the annealing temperature of the wire to preserve the half-hard temper of the stranded wires.

The stranding arrangement is similar to that of the conventional, concentric strand conductor using bare wires. However, the electrical performance of the enameled cable according to the present invention is superior to the conventional concentric stranded conductor and, in fact, is essentially equivalent to the commonly used segmental strand when installed in steel pipe.

Conventional concentric strand has a high skin effect and high proximity effect. Segmental (i.e. 4-segrnent) strand reduces both skin and proximity effects to approximately 40% of the concentric strand values in air. However, when the-segmental strand is operated in steel pipe, the values are doubled over that in air.

In the case of enameled concentric strand conductor according to the present invention, the skin effect remains the same as conventional concentric strand but the proximity effect is eliminated. Further, in steel pipe, the skin effect of enameled concentric strand is not increased. Thus, in steel pipe the cumulative skin-proximity effects of enameled concentric strand is of the same order of magnitude as segmental strand.

In addition to the fact that the polyurethane enamel may be baked at a temperature which is lower than the temperature which would anneal the individual wires, the polyurethane enamel has the important advantage that Patented Jan. 5, 1965 it will decompose on application of a temperature of the order of molten solder (approximately 600 F.) and the products of decomposition have a fiuxing action. Thus, the concentrically stranded enamel conductor may be spliced simply and solder bonds eiiected with the usual equipment.

It is not necessary to enamel all of the Wires. It is only necessary that the individual wires be insulated one from the other. Thus, for example, the center conductor 16 may be bare; all wires 18 of the 6-wire layer should be enameled; the wires 20 in the lZ-Wire layer may be alternating bare and enamel; all wires 22 in the 18 w'ire' layer should be enameled; the wires 24 in the 24-wir'e layer may be alternating bare and enamel; all wires 26 in the 30-wire layer should be enameled; and the wires 12 in the 36-wire layer may be alternating bare and enamel. The bare wires in the 36*wire layer provide electrical contact to the electrical conductive shield which is conventionally applied over the conductor. The enamel will, of course, isolate the copper in the individual wires from the oil, thus preventing deleterious action on the oil. In such applications, the bare wires should be aluminum, tinned copper or copper coated with a lead-tin alloy to prevent contact of the copper with the oil.

In FIG. 2 there is shown, in schematic form, a typical arrangement for wire fabrication.

The wire 2% is drawn to therequisite size by the drawing die 30. The drawing operation will usually consist ofa plurality of draws with intermediate annealing as required. The drawing operation is so arranged that the wire is at a half-hard temper when it is drawn to the required size.

The Wire is then passed through an enamel applicator 32 for application of thin enamel coat to the wire. The applicator 32 is preferably of conventional construction, such as a magnet wire enameling machine.

The enamel must Care at a temperature well below the temperature which would anneal the wire. Further,'

the enamel must decompose at soldering temperatures to allow easy splicing of the cable. At the present, only the'p'olyurethane enamels possess these attributes. The typical polyurethane enamels available consist of a mixture of a blocked isocyanate resin, a polyester, and an appropriate solvent. The blocked isocyanate is an addition product of 3 mols toluene diisocyanate, 1 mol of hexanetriol, and 3 mols of phenol. The polyester used is made from 2.5 mols adipic acid, .5 mol phthalic acid and 4 mols of a triol. The proportions of the two components are 233 parts of the polyester to 100 parts isocyanate.

The liquid enamel polymerizes and forms the polyurethane film on baking immediately after coating. The blocking agent of the isocyanate is removed at temperatures in excess of 140 C. at which time polymerization can commence.

The wire is baked in an oven 34- and coiled on reel as. g The reel is of conventional size for use with stranding machines. The temperature must be above the curing temperature of the polyurethane enamel but below the temperature which would temper the copper wire. For example, using a typical 24-ft. long oven, a wire speed of 14 ft./min, and an oven temperature of 560 F., No. 8 A.W.G. wire was exposed to the oven temperature for four passes or for a time'of about 400 seconds.

Some commercially available polyurethanes contain nylon. Such polyurethanes are also satisfactory as long as the curing temperature is low and the cured enamel will decompose at the temperature of molten solder. For the purpose of this application, the term polyurethane is not to be limited to the specific composition described but includes the commercially available polyurethane compositions of the requisite low baking temperature and decomposition characteristics.

The enameled wire may then be stranded in a concentric stranding machine shown in FIG. 3.

in FIG. 3 there is shown in schematic form a typical assembly operation for fabrication of the concentrically stranded conductor. The central strand 16 is lead through a concentric stranding machine 32-3 consisting of a plurality of wire stranding heads 40 to apply the desired number of concentric wraps of copper wire to the central wire from the wire reels 36 carried by each head.

Each reel 36 may carry enameled wire. Alt'ernately, as noted above, alternate reels may carry bare wire which wire may be aluminum, copper coated with tin, or copper coated with a lead-tin alloy. Coating of the copper wire is preferred to prevent contact of the bare copper with oil which would adversely affect the oil.

Thus, by this method the conductor can be formed 3 with the requisite high tensile strength and with the desirable attributes of individually insulated wire.

This invention may be variously embodied and modi- I tied within thescope of the subioined claims.

What is claimed is:

l. A cable conductor tor pipe cable which has good solderability and a combined skin efiect and proximity effect loss much lower than conventional concentrically stranded cable in the same environment, said conductor comprising concentrically stranded copper Wires, each of said wires having a halt-hard temper, and each of said wires being insulated from adjacent wires by an insulation layer of cured polyurethane enamel which cures at a temperature below the copper annealing temperature and which, after being cured, will decompose at a ternperat'ure of the order of molten solder to provide a fluxiug action and facilitate soldering.

' 2. A cable conductor. in accordance with claim 1 in which non-adjacent wires in the outer layer of wires are bare.

' 3. A cable conductor in accordance with claim 1 in which alternate conductors in each alternate strand layer are bare.

4. A cable conductor in accordance with claim 3 in which said bare conductors are aluminum.

5. A cable conductor in accordance with claim 3 in which said bare conductors are copper coated with tin.

6. A cable conductor in accordance with claim 3 in which said bare conductors are copper coated with a lead-tin alloy.

References Cited by the Examiner UNITED STATES PATENTS 1,173,190 2/16 Hoopes 174128 1,384,448 7/21 Gilbert et al 205-21 2,066,525 1/37 Gilbert 174-128 2,098,163 11/37 Reed 174128 2,278,729 6/45 Schmidt 205-21 3,027,418 3/ 62 Peterson 174-72 FORETGN PATENTS 437,3 l0 10/35 Great Britain.

OTHER REFERENCES Mechanical Engineers Handbook, Kent, eleventh edition, pages 4-09 and 410.

JOHN F. BURNS, Primary Examiner.

JOHN P. WILDMAN, Examiner. 

1. A CABLE CONDUCTOR FOR PIPE CBLE WHICH HAS GOOD SOLDERABILITY AND A COMBINED SKIN EFFECT AND PROXIMITY EFFECT LOSS MUCH LOWER THAN CONVENTIONAL CONCENTRICALLY STRANDED CABLE IN THE SAME ENVIRONMENT, SAID CONDUCTOR COMPRISING CONCENTRICALLY STRANDED COPPER WIRES, EACH OF SAID WIRES HAVING A HALF-HARD TEMPER, SAND EACH OF SAID WIRES BEING INSULATED FROM ADJACENT WIRES BY AN INSULATION LAYER OF CURED POLYURETHANE ENAMEL WHICH CURES AT A TEMPERATURE BELOW THE COPPER ANNEALING TEMPERATURE AND WHICH, AFTER BEING CURED, WILL DECOMPOSE AT A TEMPERATURE OF THE ORDER OF MOLTEN SOLDER TO PROVIDE A FLUXING ACTION AND FACILITATE SOLDERING. 